This invention relates to mountain climbing equipment and techniques, and more particularly, to apparatus and methods for braking a climber's descent while rappelling.
In the art of mountain climbing it is frequently desireable for a climber to rappel, that is to move down a steep incline or overhang of a mountain suspended by a rope. In the fundamental rappelling operation the rope is supported from above the climber and wrapped around his body, usually under the left thigh and over the right shoulder. As the climber moves down the rope, playing it out with his hands, the rubbing of the rope against his body produces braking friction which tends to reduce the speed of his descent. However, it is often difficult for the climber to control his descent merely by wrapping the rope around his body and holding it with his hands. Moreover, the use of the climber's hands and body against the rope to brake his descent tends to cause injury to the climber due to the friction, and this tendancy limits the speed with which the climber may descend the mountain.
Other activities such as fighting fires and washing windows of tall buildings also frequently require a person to descend from a high place such as a building with a rope, and the aforementioned basic problems of rappelling arise in these activities as well. A number of devices have been designed for use in these activities to alleviate the problems encountered in descending by rope from a high place. Such devices are illustrated, for example, by Hobbs U.S. Pat. No. 3,678,543 showing a controlled personal descent device which utilizes a generally C-shaped hook and an enclosed-loop brake bar which slips over the hook to extend from side-to-side thereof, one end of the brake bar covering the opening on one side of the C-shaped hook. The hook is attached to the person by a ring and harness, and the supporting rope is threaded through a space defined by the brake bar and the top end of the hook, over the brake bar and back through a space defined by the brake bar and the bottom end of the hook. Alternatively, the rope may be wrapped in some other manner around the hook to further increase the friction surface between the hook and the rope. When longitudinal tension is placed upon the lower end of the rope, the friction produced by the rope's traveling through the hook and over the brake bar slows the descent of the person. Hobbs U.S. Pat. No. 3,757,901 discloses a similar, but more complicated, braking apparatus which includes a body member with two C-shaped portions each of which may be closed by a gate, and a C-shaped brake bar which slips over the body member extending from side-to-side thereof. Such specialized braking devices are not readily adaptable for use in mountain climbing because they may only be used effectively for the single limited purpose for which they were designed; therefore they would add weight to the climber's load which may not be efficiently utilized. Also, the safety of the device disclosed in U.S. Pat. No. 3,678,543 is limited since the hook does not form a fixed closed loop around the supporting rope, and while the gate of the device shown in U.S. Pat. No. 3,757,901 would reduce the likelihood of inadvertent release by providing such a fixed closed loop, the gate is relatively complicated to use and thus undesireable for the already difficult circumstances of mountain climbing.
In rappelling while mountain climbing braking is often accomplished utilizing a carabiner in combination with a brake bar attached thereto. The carabiner usually comprises an elongate closed loop made of strong, light metal having a circular cross-section with a swinging, spring-loaded gate formed in one side such that the carabiner may be rapidly attached and detached from various supporting implements. The brake bar typically comprises an elongate member having an aperture at each end, one of which is slotted from opening-to-opening, and the bar is attached to the carabiner such that it runs from side-to-side thereof, a portion of the loop of the carabiner being disposed in each of the apertures. One end of the carabiner is attached to the climber by some appropriate means, such as another carabiner attached to a loop of strong web-like material worn by the climber, and the suspending rope is threaded through this apparatus in a manner similar to the aforementioned prior art. As the mountain climber descends by the supporting rope he brakes and controls his descent by placing longitudinal tension on the portion of the rope below the carabiner to produce braking friction.
The use of a single carabiner and a brake bar by mountain climbers provides the advantages of efficient use of materials since a mountain climber typically carries a number of general purpose carabiners which are used for support and guiding ropes during climbing, thereby minimizing the weight carried, and safety since this arrangement is particularly adapted by its simplicity to the arduous circumstances of technical mountain climbing where errors may be very hazardous. On the other hand, the single carabiner utilized in this arrangement may break or come loose from the brake bar because this arrangement places a high transverse loading on the carabiner, which it was not designed to withstand, thereby presenting an extremely hazardous condition, and occasionally more braking friction is required than is readily provided by this apparatus.